Pointing device with solid-state roller

ABSTRACT

A solid-state roller on a pointing device with enhanced features. The solid-state design described herein allows the sensor to be placed on any shape of surface, such as one that has curvature in two directions. In one embodiment, a trench or downward curve contains sensors for detecting finger movement. The user&#39;s finger can thus bend about a knuckle in a curved motion to activate the sensor, requiring little or no movement of the finger up and down. The solid-state sensors can be of one of a number of designs. In one embodiment, multiple electrodes are contacted by a finger as it moves. Each electrode is coupled to a capacitive detection circuit, for detecting the change in capacitance as the electrode is contacted by the finger.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/025,838, filed Dec. 18, 2001, which claims the benefit of U.S.Provisional Application No. 60/258,133, filed Dec. 22, 2000, whichdisclosures are incorporated herein in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a solid-state roller (with no movingparts) on a pointing device, such as a computer mouse.

A number of computer mice include a roller or wheel which can be rotatedby a user's finger. Typically, such a roller is used for scrolling. Oneexample is set forth in Logitech U.S. Pat. No. 6,157,369, and otherexamples are described in the background section of that patent. Some ofthe disadvantages of a roller are that it is a mechanical element, andthus subject to mechanical failure since it is susceptible to dirt andshock. In addition, its size can make it difficult to integrate intosome form factors such as a very low profile mouse.

Other patents describing a roller or wheel include U.S. Pat. Nos.5,530,455 and 5,473,344. U.S. Pat. No. 5,530,455 also describesdetermining the speed of scrolling in the mouse driver software, andswitching between line scrolling and page scrolling depending on thespeed.

Some earlier designs have proposed a touchpad on a mouse. U.S. Pat. No.5,805,144 shows a touchpad with pressure sensing. The touchpad allowsfor sensing in only one direction, and also provides tactile feedback.Touchpads on a mouse are also shown in U.S. Pat. No. 5,771,038 and PCTPublication WO91/04526.

Another patent, U.S. Pat. No. 5,555,894, shows depressions for keys andthe use of pressure sensors for detecting the bending of the fingers byusing multiple sensors on a key to detect finger movement.

SUMMARY OF THE INVENTION

The present invention provides a solid-state roller on a pointing devicewith enhanced features. In one embodiment, a capacitive sensor isprovided which uses galvanic finger contact. In particular, the fingeron an electrode acts as a switch to connect ground, through the body,the body capacitance and a capacitance connected to the electrode. Asthe finger passes from one electrode to another, movement and directionis sensed. A unique differential detection circuit is also provided,which alternately clamps a node high and then low, allowing measurementof both capacitive charge-up and discharge, to compensate forinterference.

The solid-state sensor allows multiple shapes to be used. Unlike atouchpad, which is practical to bend in only one direction, thesolid-state roller can be on a surface with curvature in more than onedirection. It can also be on either a concave or convex surface. In oneembodiment, a convex trench or downward curve contains sensors fordetecting finger movement. The user's finger can thus bend about aknuckle in a curved motion to activate the sensor, requiring little orno movement of the finger up and down. In another embodiment, the sensoris on a convex surface, such as on a side for activation by the thumb.

The solid-state sensors can be of one of a number of designs. In oneembodiment, multiple electrodes are contacted by a finger as it moves.Each electrode is coupled to a capacitive detection circuit, fordetecting the change in capacitance as the electrode is contacted by thefinger. In another embodiment, light from one side of a trench isblocked by the finger from reaching detectors on the other side of thetrench, allowing detection of the movement of the shadow of the finger.Alternately, a reflective optical embodiment is used. In anotherembodiment, capacitive coupling of the finger is detected with threeelectrodes, one of which has a zigzag shape to allow variation in theamount of the capacitance as the finger moves along the zigzag.

In other embodiments of the invention, a fingerprint optical reader canbe used to detect movement of a fingerprint over a sensor window. Thesolid-state roller can also have a cross shape, to allow both verticaland horizontal scrolling.

In one embodiment, the speed of finger movement is determined in thepointing device, rather than in a software driver as in the prior art.The signal sent to the computer multiplies the number of transitions inaccordance with the detected speed. This allows a single transition tospeed up scrolling, rather than requiring multiple reports to a softwaredriver.

Instead of the mechanical ratchet feedback of the prior art mechanicalrollers, the present invention uses other forms of feedback. Forexample, a clicking sound emanates from a speaker mounted in thepointing device. By using a speaker in the pointing device, instead ofthe computer speaker, the latency is greatly improved, giving arealistic feedback. Alternately, lights could flash in the mouse. In oneembodiment, a light used in the pointing device for decorative purposescan be flashed to indicate a notification to the user. One example wouldbe an event being monitored by the user externally to the computersystem, such as over the Internet, with the flashing light in thepointing device prompting the user.

For a further understanding of the nature and advantages of theinvention, reference should be made to the following description takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a mouse with a solid-state sensor trenchaccording to one embodiment of the invention.

FIG. 2 is a side view of the mouse of FIG. 1.

FIG. 3 is a diagram of a cross-shaped trench for horizontal and verticalscrolling in an embodiment of the invention.

FIG. 4 is a diagram illustrating the pointing sensor apparatus inconjunction with the solid-state roller, and a speaker, in oneembodiment of the invention.

FIGS. 5A-5C illustrate different electrode arrangements according toembodiments of the invention.

FIG. 5D is a waveform diagram of a sensor output for an electrodearrangement as shown in FIG. 5A.

FIG. 6 is a block diagram of a capacitive detection circuit in oneembodiment of the invention.

FIGS. 7A and 7B are block diagrams illustrating the operation ofcapacitive sensing.

FIG. 8 is a circuit diagram illustrating a capacitive sensing circuitwith a clamp-down circuit.

FIG. 9 is a timing diagram illustrating the operation of the circuit ofFIG. 8.

FIG. 10 is a circuit diagram illustrating a capacitive sensing circuitwith a clamp-up.

FIG. 11 is a timing diagram illustrating the operation of a circuit ofFIG. 10.

FIG. 12 is a diagram of a capacitive sensing circuit having bothclamp-up and clamp-down capability.

FIGS. 13, 14, and 15 are timing diagrams illustrating the operation ofthe circuit of FIG. 12.

FIG. 16 is a diagram of a capacitive sensing circuit according to anembodiment of the invention.

FIG. 17 is a timing diagram illustrating sampling in pairs during aperiod of the power supply frequency.

FIG. 18 is a diagram of an alternate sensor with a single-ended, zigzagelectrode.

FIG. 19 is an equivalent circuit for the embodiment of FIG. 18.

FIG. 20 is a cut-away, cross-sectional view of a finger on theelectrodes of FIG. 18.

FIG. 21A-C are timing diagrams illustrating the operation of the circuitof FIG. 18.

FIG. 22 is a timing diagram illustrating the use of phase modulation forthe circuit of FIG. 18.

FIG. 23 is a diagram illustrating the embodiment of FIG. 18 using aquadrature structure.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Curved Solid-State Roller

The solid-state roller of the invention allows the roller to be placedon any shape housing. A trench or other convex shape could be used.Alternately, a concave shape could be used. A concave shape could beused for placement of the sensor on the side of a mouse, for activationby a thumb. The solid-state design described herein allows the sensor tobe placed on any shape of surface, such as one that has curvature in twodirections. Thus, it could simply track the contour of the mouse orother pointing device. This allows a pointing device to be designed foraesthetic or ergonomic reasons, and a solid-state roller can be addedwithout requiring the shape to change.

Various shape implementation are covered in the invention. A curvedtrench with curvature matched to the hand creates a support surface thatis lower than that of the two neighboring surfaces. This reduces thestrain on the scrolling finger. Alternatively, the three middle fingertips rest over support surfaces having all similar heights, but the tipof the scrolling finger, when scrolling and leaving its original restposition, will travel over a trajectory that is below the plane definedby the two neighboring fingers, by entering a support surface in recesswith this plane. For example, the scrolling finger tip follows atrajectory defined by the rotation of the finger around its middlejoint.

FIG. 1 is a perspective view of a mouse 10 having buttons 12 and 14.In-between the buttons is a convex area, or trench, 16 which can receivea user's finger. At the bottom of the trench are electrodes 18, 20 and22. The movement of a user's finger either forward to back, or back toforward can be detected (as will be described later), and appropriatescrolling or other signals can be sent to a host computer. Alternately,other solid-state sensors than the electrodes shown could be used. Forexample, light emitters could be mounted on one side of the trench, withdetectors on the other side, and the trench being transparent ortranslucent.

FIG. 2 is a side view of mouse 10 of FIG. 1. Shown in phantom is theoutline of the bottom of trench 16. As can be seen, the bottom follows acurvature, starting out at the front at a particular level, becomingdeeper, and then becoming more shallow towards the back of the mouse. Inone embodiment, this curvature traces the arc of a typical user's fingerbending about the second knuckle while the hand is on the mouse. Thesecond knuckle is the second knuckle away from the tip of the finger.The curvature in one embodiment takes into account the slight bending ofthe first knuckle as well, but with more than ⅔ of the bending movement(dictating the shape of the arc) coming from the second knuckle. In oneembodiment, the arc of the trench is matched to the curving of the indexfinger or forefinger. This arc eliminates the need for the user to liftthe finger up to activate a roller. Alternately, the arc can be lesssteep, requiring a slight lifting of the finger as well, but lesslifting than what is required for a mechanical roller or a solid-statetouchpad on a surface without a trench.

FIG. 3 is a diagram illustrating a dual-trench arrangement in which avertical trench 36 is provided for up and down scrolling movement, whilea horizontal trench 38 intersects with it for horizontal scrollingmovement. Electrodes such as electrodes 37 and 39 can be used to detectfinger movement in both directions.

In another implementation, the finger rests in a trench wide enough toaccommodate the finger, but not too wide in order to guide the finger inthe direction of detection. Position detection is achieved with help ofan array of light sources, or a single distributed light source, on oneof the trench sides, and an array of light detectors located on theother side. Presence of the finger in the trench is detected from thereduced response in the detector directly facing the finger, or fromcombining responses from all detectors and determining by interpolationits minimum. Alternatively, a binary response from the light detector,either absolute (“light is above or below a given threshold, includehysteresis”), or relative with neighboring detector (“light islarger/smaller by a given factor than neighbor, include hysteresis”) canbe used. Similarly as in the previous electrode implementation, motioncan then be computed based on the “on-off” and “off-on” transitiontimings with correct relative phase shifts.

Integration with Other Elements of a Mouse

FIG. 4 is a diagram illustrating some of the internal components of amouse 10 incorporating the present invention. In the embodiment shown,trench 16 has a light-emitting diode(s) 40 on one side, and a multipleelement photodetector 42 on the other side. By having the multipleelement photodetector be able to detect separately when light impingeson different elements of it, the movement of a finger can be tracedthrough a translucent or transparent trench wall. The LEDs arecontrolled by a microcontroller 44, which also monitors the detectorsignals.

The microcontroller also provides control signals to a speaker 46, forproviding feedback sounds, such as a clicking sound, synchronized withthe movement of a finger through trench 16. By including speaker 46 inthe mouse, the latency of sending signals to the computer, and havingthe computer generate sounds through speakers connected to the computer,is avoided. This provides a more realistic, real-time feedback to theuser. The desired clicking sound can be simply generated by themicroprocessor using an appropriate square wave output to the speaker,which is simply a series of high and low output levels. The simplestimplementation is a single high/low or low/high transition.

FIG. 4 also illustrates other standard components of a typical mouse,including a ball 48. Biased against ball 48 are rollers 50 and 52 whichhave attached slotted wheels 54 and 56, respectively. The slotted wheelspass between emitter/detector pairs 58 and 60, respectively.Alternately, another pointing sensor could be used, such as the opticalsensors available from Agilent or others. Finally, FIG. 4 shows multipleswitches 62 which are activated by the buttons on a mouse. Thecommunications to a host computer can be done over a serial interface64, or with a wireless transmission.

Multiple Electrode Arrangements

FIG. 5A is a top view of trench 16 of FIG. 1, illustrating a twoelectrode embodiment. Two electrodes, designated 1 and 2, are shown. Inthis embodiment, the capacitive coupling of a finger to the electrodecan be detected. By detecting which electrode is contacted first, it canbe determined in which direction the finger is moving. This can be usedto scroll or zoom in or out in the appropriate direction on thecomputer. Alternate uses of the movement of the finger may also be used.

FIG. 5B shows an alternate embodiment using multiple electrodes in arepeating pattern. As shown, the first and fourth electrodes areconnected together as electrode 1. The second and fifth electrodes arenumber 2, and the third and sixth are number 3. This arrangementprovides for more preciseness, while limiting the number of electrodes,and thus the amount of wiring needed to connect to the electrodes on thesensor.

FIG. 5C shows yet another alternate embodiment, in which multipleelectrodes are connected to only two wires, to form connected electrodes1 and 2. As shown, the electrodes overlap in a vertical direction, sothat a user's finger will contact electrode number 2 before leavingelectrode number 1. The movement of the finger generates two signals inquadrature, from which the direction is determined from the sign of thephase shift. A more detailed description of such a quadrature detectioncan be found in U.S. Pat. No. 5,680,157. The varying amount of voltagedetected on a particular electrode shows the direction of movement, andcan support a more fine-tuned determination of where the finger is,especially in the area that would be between electrodes in the otherembodiments. The inventors have discovered, however, that the embodimentof FIG. 5A, the simplest, is sufficient for many applications.

FIG. 5D illustrates example waveforms generated from the touching ofelectrode 1 and electrode 2 of FIG. 5A. The waveforms would be theoutput of a comparator 34 in FIG. 6 below, for example. A first pulse 13shows the finger in contact with the first electrode, with the risingedge corresponding to when the finger first touches the electrode, andthe falling edge corresponding to when the finger leaves the electrode.The same applies for pulse 15, corresponding to the second electrode.Note that there is some overlap, and that the direction of fingermovement can be determined from which electrode is contacted first(alternately, or in addition, which electrode the finger leaves last).Pulses 17 and 19 illustrate the finger moving in the other direction.Pulses 21 and 23 illustrate the finger remaining on the second electrodeafter moving, which can be used to provide a continued scrolling in thesame direction.

In the embodiments above, the dedicated surface for sensing is typicallylocated in place of the wheel, though other locations can be envisaged,for example below the thumb rest position. In one implementation, anumber of sensitive electrodes are inserted, or molded over thesensitive surface. While the minimum number of electrodes is two, alarger number can be used in order to accommodate for a large sensitivearea. In one implementation, finger movement indicative of the userdesire to scroll is detected by an appropriate succession of on-off andoff-on transitions in the electrodes, all with a relative phase shiftconsistent with the physical locations on the surface. In addition,speed constraints can be enforced by measuring the rate of electrodetransitions, allowing for example, the discarding of excessively slowscrolls while improving on reliability, or allowing the application oflarger document scrolls for movements at large speeds. The electrodesshape and spacing are matched to the finger dimension for comfort anddetection robustness.

Connecting the electrodes with a period N creates a spatially periodicalsensitive structure allowing a reduction in the electronics by a factorin the order of N, thus allowing larger sensitive surface at same cost.Typically, N is 3 to 4 but a value N of 2 is also possible if a gap isforeseen between each electrode pair and if there is a degree of spatialoverlap within an electrode pair.

Capacitive Detection Circuit

FIG. 6 is a block diagram of the capacitive detection circuit connectedto each electrode. In the example shown, an electrode 1 is connected toa sensing capacitor 24 and a pull-up/pull-down resistor 26. In practice,the capacitor may be simply a gap in the wiring to the electrode. Thisgap can be created in a number of ways. A Mylar (Dupont's trademark forpolyester foil) sheet can be used as a dielectric between the wiringconnection and the electrode. This provides a well characterizeddielectric, with a well characterized thickness, wedged between theconductor's terminal and the electrode, so that the resultingcapacitance is well determined in spite of differences in tolerancesduring manufacturing. A flexible PC board could be used, with theflexible substrate itself causing the gap, i.e. the dielectric, betweenthe electrode and the wiring. In one embodiment, the gap is about 50microns, although the gap used can vary widely depending on thedielectric, etc. In one embodiment a wire is simply not stripped afterit is cut, leaving its insulation intact up to the end. Then it isinserted through a hole in the electrode that has the same diameter asthe insulation's external diameter. Or the electrode may be made of twopieces that are assembled around the insulated wire so that this issurrounded by the electrode. This makes a cylindrical or tubularcapacitor at no material cost, where the wire jacket is the dielectric.

A clamp-up circuit 28 and clamp-down circuit 30 allows the node to beconnected to the supply voltage or ground, respectively. These clampcircuits are under the control of a controller 32. The controller canthus clamp the voltage low, and then measure the time for the capacitorto charge up. Alternately the voltage can be clamped high, and then,after releasing the clamp, the time for the voltage on the capacitor todischarge can be measured. The voltage on the capacitor is provided asone input to a comparator 34, which compares to a voltage threshold, andprovides an output to controller 32. The operation of the circuit andthe theory behind it will be described in more detail below. Otherimplementations are possible, rather than using discrete components,such as an ASIC or the standard I/O of a microcontroller having abuilt-in comparator, or even using the inherent voltage threshold levelof one of its input buffers.

In one embodiment, the driver for an I/O pin in a microcontroller can beused as a clamp-up or clamp-down circuit. An input buffer of themicrocontroller could be used as the comparator. Such a design may notbe as accurate, but could be sufficiently accurate, and would reduce thenumber of components and thus the cost. The comparator could be anycircuit which performs a comparing function, including an appropriatelyconfigured amplifier. The comparator need not have two inputs, but coulduse an internal node for the threshold.

FIGS. 7A and 7B illustrate the conceptual operation of an embodiment ofthe capacitive detection of the present invention. A capacitive sensoris generally intended to detect the presence of an object when it iscloser to a given distance, i.e. when either the capacitance of oneelectrode to the earth ground or the mutual capacitance between twoelectrodes of the sensing circuitry reaches a given value (threshold).

This working principle is less practical when it comes to implement atouch sensing function. The threshold would have to be carefullyadjusted so that it would be reached at the same time as the fingertouches the surface of the sensor. Therefore an easier approach can beadopted where the contact of the finger leads to a clear step incapacitance, much easier to detect, possibly without any adjustment.

The solution in one embodiment of the invention consists in building agalvanic sensor, shown in FIGS. 7A and 7B, where the finger comes incontact with one armature of a built-in sense capacitor 66, thus pullingit to the earth ground through the existing body to ground capacitance68 that comes in series (contact is illustrated by “switch” 72,representing contact by a user's finger). Provided that the built-incapacitor has a much lower capacitance than the body to ground coupling(which ranges from 100 to 500 pF), the contact can easily be detected bya capacitive sensing circuitry 70, in the form of the sudden“apparition” of the built-in capacitor when the user touches itsexternal armature. The rest of the time, when nothing touches thegalvanic sensing area, the built-in capacitor remains “invisible” forthe rest of the electronics. Please note that the sensing capacitorpreferably is as close as possible to the sensing electrode, so that nosignificant parasitic capacitance is present between the discretecapacitor and the electrode, which would make the sensing capacitor“always visible” thus ruining the touch sensing function. In oneembodiment, the “discrete” capacitor 66 is simply a gap within theconnection from the electrode to the circuit board containing the sensorcircuit 70.

There are several ways of making capacitive sensing circuitry 70, fromthe simplest and cheapest RC charge or discharge time measurement to themost complicated tuned oscillator or filter system. One simpleembodiment uses a free running RC oscillator where C is the sensingcapacitor and a microcontroller repetitively counts the oscillationperiods that occur during a given time window. A decrease in the numberof counted periods by at least a given value means a finger has beenplaced on the electrode, while a minimal increase of accumulated countsis interpreted as the finger having been released from the electrode. Noadjustment is needed; only the minimal difference of counts is to be setin accordance with the value of the capacitor used as the sensingelement.

Another embodiment, instead of relying on RC exponential charging, usesa current source instead of a resistor, to give linear voltage ramps.With linear voltage ramps, a dual-ramp compensation scheme can beeffective (see discussion below). A linear ramp allows compensation forlarge perturbations, and allows for more flexibility in thresholddistance from the starting voltage.

Another embodiment uses an inexpensive solution, although thisunfortunately suffers from bad noise immunity, especially against mainssupply, which may be present in a large amount on the human body we wantto detect. These low frequency signals are not well drained to earthground through the 100 to max. 500 pF of the body to ground capacitance.We therefore prefer to get rid of the low frequency noise interferenceas much as possible, which will be described below.

In order to be able to implement these noise rejections we use amicrocontroller, thus finally rending the simplest solution as effectiveas the most sophisticated ones, but still cheaper.

Basically, the embedded algorithm compares the RC time discharge to areference time threshold in order to determine whether a finger ispresent or not. C is the sum of the inherent parasitic capacitance andthe sensing capacitance, while R is the pull-up or pull-down resistorthat drives the sensing line. The time threshold is automaticallyreadjusted each time after the finger is detected as put on or releasedfrom the sensor, in order to compensate for the parasitic capacitances(which do not vary with the finger present or not). Only the timedifference—the function of the minimal difference in capacitance we wantto detect (4 pF or more)—is hard coded. Thus the system needs no factoryadjustments.

FIG. 8 illustrates the principle used in an embodiment of the capacitivesensor 70 of the invention. FIG. 8 shows the elements of FIGS. 7A and7B, with the galvanic contact switch 72 being the contact electrode 76and finger 78. Sensor 70 includes an optional protection resistor 80 inseries to an input node 81 of a comparator 82. Node 81 is clamped toground via a switch 84 for initialization. When switch 84 is open, node81 is charged through pull-up resistor 86. This charging is done in atime determined by the time constant of resistor 86 and the capacitances66 and 68, along with the parasitic capacitances as shown. In additionto parasitic capacitance 74, a parasitic capacitance 88 is shown. Thethreshold at the second input of comparator 82 is set to two thirds ofthe supply voltage, Vcc. FIG. 8 also shows protection diodes betweenground and node 81, and between Vcc and node 81, respectively. Otherthresholds could be used depending on the embodiment. ⅓ and ⅔ are onlyillustrative. If the thresholds are the same amount above and below thelow and high supply voltages, the same time period can be achieved fordischarging and charging. However, the thresholds could be differentamounts from the supply voltages, and simply require an adjustment totake into account the difference in the discharge and charge times.

FIG. 9 illustrates the timing for both a no finger condition, and afinger condition. Clamp 84 is first closed, to bring the voltage down toground, or zero. When the clamp is opened at a time 90, node 81 chargesup to the ⅔ threshold within a time T0. Node 81 is then grounded againat a time 92, and the switch is opened again at a time 94. At thispoint, a finger is on, adding capacitance, and lengthening the timerequired for the threshold to be reached to time T0+dTf.

FIG. 10 illustrates a similar circuit, but instead is showing the amountof time required for an input node to the comparator to be lowered froma high voltage to below a threshold. The threshold here is one-third ofthe supply voltage Vcc. In this example, the node is clamped to thesupply voltage, and then is allowed to discharge to ground through aresistor R2. Otherwise, the circuitry is basically the same as thatshown in FIG. 8, including the use of protection diodes between groundand node 81, and between Vcc and node 81, respectively.

FIG. 11 illustrates the timing with no finger and with the finger,showing again that a longer time is required to discharge thecapacitance when the finger is on the sensor.

FIG. 12 illustrates essentially a combination of the two approaches ofFIGS. 8 and 10. Since the output of comparator 101 will either be highor low from the previous cycle, this output can be used to both be thesource for pulling up (logic 1 output) through resistor 103, or pullingdown (logic 0 output) through the same resistor. Also, the same outputcan be fed back to set the threshold, using resistors R3, R4 and R5. Thethreshold is set to 0.66 Vcc for a logic 1 output, and to 0.33 Vcc for alogic 0 output, using the same resistors.

The arrangement of FIG. 12, shown in more detail in FIG. 16 below, usestwo clamps, allowing the capacitor to alternately charge up from ground,or discharge from the supply voltage. By using both, interference, suchas from the power supply frequency, can be reduced, as explained below.

FIG. 13 illustrates a capacitor charge and discharge cycle with nofinger (100), and a charge and discharge cycle with a finger on thecontact electrode (102). With no finger, the input node to thecomparator is clamped to ground, and the lower clamp is opened at apoint in time 104. The capacitance charges up until it crosses the upperthreshold at a point in time 106, triggering the comparator output.Subsequently, the node is clamped high at a point in time 108, and thenthe clamp is opened at a point in time 110 to provide a discharge cycle.At time 112, the lower threshold is crossed, again triggering thecomparator output. The voltage is then clamped down to zero again at apoint 114, and the cycle repeats. During the second cycle illustrated bycurves 102, a finger is on, and the times will be different, resultingin a longer charging time and longer discharging time. In oneembodiment, cycle 102 is two milliseconds after cycle 100. Although T0is shown as the same for the rising and falling (charging anddischarging) times, this is not necessary.

FIG. 14 illustrates a curve 116, similar to the curve 100, when nofinger is on the electrode. Curve 118 illustrates a finger on, with theaddition of noise interference represented by dTm. Thus, as shown, thecharge up time will be T0+dTf−dTm, where T0 is the time without afinger, dTf is the additional time caused by the finger, and dTm is thenoise interference. During a discharge cycle, the components are thesame, except in this instance the interference is an additive term.Thus, by combining the two and using a sum result, the noise will cancelout. If the delay from the rising to the falling ramp is short comparedto the period of the main power supply frequency, the interference willbe the same on both ramps.

FIG. 15 illustrates another example, again showing a curve 120 with nofinger, and a curve 122 with the finger on. In this instance, the noiseis additive during the capacitive charging, and subtractive duringcapacitive discharging, with the same effect of canceling out when thetwo are combined.

FIG. 16 is a circuit diagram illustrating a capacitive sensing circuit,such as shown in block form in FIG. 4 and in FIG. 12. FIG. 16 has twoinputs, 130 and 131. These correspond to two separate electrodes, eachwith their own capacitance connected. Input 130 is connected to oneinput of a comparator 132, while input 131 is connected to an input ofcomparator 134. Each of the comparators provides an output tomicrocontroller 32. The other input of each of the comparators isconnected to a resistive circuit for setting the threshold. Thethreshold is set using feedback from the output of the comparator. Thus,when the output of the comparator is a 1, the threshold will be setone-third below the supply voltage, or at a level of 0.66. When theoutput of the comparator is zero (with the output being determined bythe last transition) the feedback puts the threshold at one-third aboveground, or 0.33.

Turning to the first input 130, this is initially clamped low by anoutput from microcontroller 32 on line 136 through a resistor 138 andtransistor 140. The same output line 136 is connected to a similar lowclamp for electrode 131. When the low clamp is released, the capacitanceconnected to input 130 will charge up through a pull-up resistor 142with a high level value on line 144 as output by controller 32. Asimilar pull-up resistor is used for the circuit for input 131. Afterthe threshold is passed and the comparator toggles, the next cyclebegins with the input 130 being clamped high through a control signal online 146, through resistor 148 to transistor 150, which clamps inputnode 130 high. The same control line 146 controls a clamp-up transistorfor the circuit attached to input 131.

FIG. 17 illustrates a second aspect of this embodiment of the invention,which further reduces interference by how measurements are done comparedto a frequency cycle of the main power supply, as illustrated. Thesuccessive (dual-ramp) time measurements are added and evaluated ingroups in such a way that the remaining influence of the mains isfurther attenuated, by means of a naturally subtractive effect.

In order to achieve this, the evaluation is performed at a rate as closeas possible to the mains period (or a plain multiple of its period)during which an even number of periodic time measurements are performed.When making the periodic sum or average of these individual timemeasurements, the influence of the mains is slightly attenuated pair bypair among the samples when added. This principle is illustrated in FIG.17 for the case of eight measurements equally distributed in time duringthe mains period.

Thus, for example, measurement pairs 1 and 5 would be combined for ameasurement value, rather than simply looking at 1 or 5 alone. Since 5is at a negative portion of the main supply frequency cyclecorresponding to the positive portion of sample 1, the combinationshould make the contribution from the interfering power supply zero.Similarly, by picking samples 2 and 6, 3 and 7, or 4 and 8, theinterference from the main power supply is further canceled out. Thisinterference in particular can be picked up by the human body andreflected in the capacitance generated by the finger contact.

The average mains period is taken as 18 ms (EU 20 ms & USA 16.67 ms). Itcovers 9 samples, but one is the first of the next evaluation period,therefore 8 samples (four pairs) shall last 15.75 ms. Thus, in the caseof eight measurements per mains period, the sampling period is 2.25 ms.

As for the evaluation rate, it may be faster than one per mains periodin order to improve the reaction time of the sensing elements. As longas each evaluation covers the mains period, it may well be performedmore often than once per mains period, in fact it can be done up to eachtime a new measurement is performed (sliding window principle).

FIGS. 18-23 illustrate another embodiment of an electrode for sensingfinger capacitance according to the invention. FIG. 18 shows threeelectrodes, 160, 162, and 164. Electrodes 160 and 164 are provided withpositive and negative signals (signals in phase opposition), from whichthe electrode 166 can sense more or less of each one, as a function ofthe finger's position. Sensing is done on a node 166 connected toelectrode 162. Electrode 164 has a sawtooth on one side, producing amodulated electrode. In the example of FIG. 18, this sawtooth isone-sided.

FIG. 19 shows the equivalent circuit diagram, with two capacitors 172and 174, whose value is varied by the location of the finger. Bymeasuring a current or injected charge into the sense node, theimbalance of the capacitance can be determined with positive andnegative signals that are 180° shifted. Referring to FIG. 20, a cut-awayview is shown of a finger 171 with capacitances C1, C2 and C3 toelectrodes 160, 162 and 164, respectively. The electrodes are on asubstrate 173 and are covered by a dielectric 175. The showncapacitances combine to form capacitances 172 and 174 as shown by theformulas in FIG. 19. A dotted line 177 in FIG. 20 illustrates thevarying width of electrode 164 due to its sawtooth shape.

FIGS. 21A-C illustrate the modeling of Cpos and Cneg as a function of X(distance of movement of the finger). The amount of effective couplingwhen the finger partially covers the linear electrodes depends on thesize of the finger. A purely periodic modulation with period T will notbe detected if the finger dimension is a multiple of W. In order toavoid this rare effect, the modulation M(X) of the sawtooth is a phasemodulated signal with ideally random modulation, or at a very lowfrequency, such as the phase-modulated signal 176 in FIG. 22. Thesensing current can be measured synchronously, or any other method. Bydetecting zero crossings, peaks (maximum or minimum), an indication ofthe finger movement by movement of T is possible (or the phase-modulatedvalue of T).

Detection of the sign, or direction of finger movement, can bedetermined using a quadrature structure such as shown in FIG. 23. Byquadrature decoding of the sensing signals, the sense_P and sense_Qsignals can yield the movement direction. In the example of FIG. 23,with a separation of the outer electrodes of less than 4 mm, with T=1mm, a 30 mm pad, of width 4 mm, could possibly obtain a resolution of1%. Sense_P and sense_Q are excited and read out alternately in atime-multiplexed sequence in order to prohibit excitation and couplingfrom the other phase (Q, respectively P).

Resistive Pad

In another implementation, a single dimension resistive pad, using forexample the force sensing resistance technology by Interlink, is used asthe sensitive region. By computing the resistance between the currentinjecting node and the contact points at opposite ends of the pad, bothposition of finger and pressure of finger can be extracted. A change ofposition by a given, and possibly programmable, relative amount willtrigger the document scrolling up or down by n lines. Finger pressureinformation can also be used for other functions such as scrollingfactor, zoom factor, or others. For example, a movement with highpressure will result in a large document scroll, while a small pressuremovement will scroll the document very slowly.

Fingerprint Sensor

In a last implementation, optical detection is used to detect the fingermovement. The finger is in contact with a transparent window while beingilluminated by a light source. High-contrast fingerprints are obtainedthanks to frustrated total internal reflection; the fingerprints arethen imaged onto a linear photosensitive array. Cross-correlationbetween a reference (initial) fingerprint image and the currentlymeasured fingerprint image indicates the amount of movement thatoccurred since the reference image was taken. When enough movement isregistered, the currently measured fingerprint image is used as thereference image for the next cross-correlation computations.Alternatively, the photoarray/correlation system can be replaced by aposition sensing device (psd), a component delivering the position of alight spot over a linear array. In this last implementation, the lightspot is simply the portion of the finger that is illuminated by thelight source and imaged onto the psd—position sensing device.

Tactile or Sound or Visual Feedback

In all systems, the solid-state roller is enhanced with feedback.Tactile feedback is obtained by embedding either texture or periodicalprofile onto the sensitive area. The embedded texture/profile hasamplitude and spatial frequency content matched to the 3D tactileperception of a finger moving at typical scrolling speed (3D relates tospatial perception+temporal—that is, moving—perception). Sound feedbackis obtained by generating one or more “click” sounds whenever a movementcreates a document scroll by one or more lines. The sound is providedthrough a speaker in the mouse itself, avoiding the delay involved inrequesting the computer to generate sound. The sound can be generated bysimply connecting an output of a controller to the speaker, with eachrising or falling edge creating a click sound.

Similarly, visual feedback is applied by switching on a LED or otherlight source whenever a scrolling movement is registered. In oneembodiment, a light used in the pointing device for decorative purposescan be flashed to indicate a notification to the user. One example wouldbe an event being monitored by the user externally to the computersystem, such as over the Internet, with the flashing light in thepointing device prompting the user.

Finally, in units implementing vibration/force feedback mice such asiFeel mice by Logitech, vibration/force feedback can be applied,typically in form of a vibration/force impulse of short duration, foreach scrolling movement.

Scrolling Speed, Scroll Repeat

In one embodiment, the speed of a transition of the finger from oneelectrode to another is measured by the controller in the pointingdevice. Depending on the speed, the controller can send a report to themouse driver in the host computer indicating 1, 2, 3 or 4 transitions.Thus, for example, a fast movement between just two electrodes can causea 4 line scroll. By doing this determination in the mouse, rather thanthe driver software, only a single transition between two electrodes isneeded to determine speed, rather than multiple transitions. This allowsfor faster response time to the desired scroll speed, and also allowsthe function to be implemented with only two electrodes on the mouse.

Fatigue generated when scrolling a large document can be avoided byusing the scroll-repeat feature of the invention. After an initialscroll, defining both the scroll direction and amplitude, ascroll-repeat can be activated simply by letting the finger rest in themovement final position without lifting the finger at end of movement.Typically, the scroll-repeat function is activated after half a secondlatency time of letting the finger remain in this position. Both thelatency and rate of scroll-repeat can be programmed to adjust to theuser taste. Additionally, for implementations providing indication offinger pressure—the fsr pad or the pressure measuring electrode touchsensing—, the scroll-repeat rate can be continuously varied as desiredby the user, under control of its finger pressure, until the scrollingfinger is released. In one embodiment, the scroll repeat function isimplemented in the controller in the pointing device. Upon detection ofa scroll movement followed by the finger resting on an electrode formore than a threshold amount of time, the controller will continuouslyprovide scrolling reports to the computer.

All of the above solid-state implementations of a roller improve on thecurrent roller wheel in that they offer a better robustness to dirt andshocks. Some implementations also offer a very compact subsystemallowing new form factors and ergonomic shapes. The sensitive surface isdesigned so that the finger is guided over a trajectory allowing reducedstrain, thus allowing for extended usage of the scrolling function.Fatigue can be further reduced by activating the scroll-repeat functionwith rate controlled by finger pressure.

As will be understood by those of skill in the art, the presentinvention may be embodied in other specific forms without departing fromthe essential characteristics thereof. For example, the pointing devicecould be connected to a TV, game console, or other device, which wouldfall within the definition of “computer” as used herein. Accordingly,the foregoing description is intended to be illustrative, but notlimiting, of the scope of the invention which is set forth in thefollowing claims.

1. A pointing device comprising: a housing for supporting a user's hand;a pointing sensor, mounted in said housing, for providing a pointingsignal; a contour on said housing for receiving a finger of said user,said contour having curvature in two directions; and a solid-statescrolling touch sensor in said contour for detecting movement of saidfinger along said contour; wherein said touch sensor includes at leasttwo electrodes, and further comprising: a circuit for detecting acontact with an electrode of the at least two electrodes, including afirst, capacitive element; a second element connected to said capacitiveelement; a comparison circuit, having an input node connected to saidcapacitive and second elements, for comparing a voltage at said inputnode to a threshold voltage; a clamp-high circuit, connected to saidnode, for clamping said node high in response to a clamp-high controlsignal; a clamp-low circuit, connected to said input node, for clampingsaid node low in response to a clamp-low control signal; a controller,connected to an output of said comparison circuit, to said clamp-highcircuit and to said clamp low circuit, for providing said clamp-high andclamp-low control signals and generating an output signal in response tomeasuring an amount of time between transitions of said output of saidcomparison circuit.
 2. The pointing device of claim 1 wherein said touchsensor further comprises: the at least two electrodes mounted in saidcontour; a capacitive detection circuit, connected to said electrodes,for detecting a change in capacitance due to a contact of said user'sfinger with said electrodes, wherein direct galvanic contact by saidfinger causes the capacitive detection circuit to connect to groundthrough said user's body.
 3. The pointing device of claim 1: whereinsaid touch sensor includes a plurality of discrete electrodes mounted insaid contour to detect movement of a finger, wherein at least first andsecond electrodes are electrically connected, with a third electrode notconnected to said first and second electrodes, said third electrodebeing mounted where a finger will contact said third electrode inbetween contacting said first and second electrodes.
 4. The pointingdevice of claim 1 wherein the second element is a current source.
 5. Thepointing device of claim 1 wherein said touch sensor provides ascrolling command in response to a movement of a user's finger acrosssaid stationary sensor, and continuing to provide said scrolling commandin response to said finger reaching one end of said stationary scrollingsensor without lifting off.
 6. The pointing device of claim 1 furthercomprising: a sensory feedback element for providing feedback to a usercorresponding to an amount of movement of said finger in said contour.7. The pointing device of claim 6 wherein said sensory feedback elementcomprises a plurality of tactile formations on a surface of saidcontour.
 8. The pointing device of claim 6 wherein said sensory feedbackelement comprises a speaker mounted in said pointing device.
 9. Thepointing device of claim 1 wherein said contour is at least partiallytranslucent, and further comprising a light emitting element mounted insaid pointing device.
 10. A pointing device comprising: a housing; apointing sensor, mounted in said housing, for providing a pointingsignal; a plurality of discrete electrodes mounted on said housing todetect movement of a finger, wherein a first electrode, included in theplurality of electrodes, is electrically connected to a second electrodeincluded in the plurality of electrodes, with a third electrode,included in the plurality of electrodes, is not electrically connectedto said first and second electrodes, said third electrode being mountedwhere a finger will contact said third electrode in between contactingsaid first and second electrodes; and a circuit, connected to saidelectrodes, for detecting contact of said finger with said electrodes.11. A pointing device for use by a user, wherein the user's bodyprovides a ground contact through the user's finger, the pointing devicecomprising: a housing for supporting the user's hand; a pointing sensor,mounted in said housing, for providing a pointing signal; a stationaryscrolling sensor mounted on said housing, said scrolling sensorproviding a scrolling command in response to a movement of the user'sfinger across said stationary sensor, and continuing to provide saidscrolling command in response to said finger reaching one end of saidstationary scrolling sensor without lifting off; wherein said stationaryscrolling sensor detects movement of the user's finger using acapacitive sensing circuit comprising a sense capacitor, wherein directgalvanic contact by the user's finger causes the capacitive detectioncircuit to connect to ground through the user's body; wherein saidstationary scrolling sensor includes: a plurality of discrete electrodesmounted in said housing to detect movement of a finger, wherein at leasta first electrode is electrically connected to a second electrode, witha third electrode not connected to said first and second electrodes,said third electrode being mounted where a finger will contact saidthird electrode in between contacting said first and second electrodes;and a circuit, connected to said electrodes, for detecting contact ofsaid finger with said electrodes.
 12. The pointing device of claim 1wherein said second element is a resistive element.
 13. The pointingdevice of claim 10, wherein the third electrode is immediately adjacentto the first electrode and immediately adjacent to the second electrode.14. The pointing device of claim 10, wherein the circuit, connected tosaid electrodes, for detecting contact of said finger with saidelectrodes, includes: a first, capacitive element, a second elementconnected to said capacitive element, and a comparison circuit, havingan input node connected to said first capacitive element and the secondelement, for comparing a voltage at said input node to a thresholdvoltage.
 15. The pointing device of claim 14, further comprising aclamp-high circuit, connected to said node, for clamping said node highin response to a clamp-high control signal.
 16. The pointing device ofclaim 14, further comprising a clamp-low circuit, connected to saidinput node, for clamping said node low in response to a clamp-lowcontrol signal.
 17. The pointing device of claim 14, further comprisinga controller, connected to an output of said comparison circuit, forgenerating an output signal in response to measuring an amount of timebetween transitions of said output of said comparison circuit.
 18. Thepointing device of claim 11 wherein said scrolling sensor comprises atleast two electrodes mounted in said contour.
 19. The pointing device ofclaim 11, wherein the circuit, connected to said electrodes, fordetecting contact of said finger with said electrodes, includes: afirst, capacitive element, a second element connected to said capacitiveelement, and a comparison circuit, having an input node connected tosaid first capacitive element and the second element, for comparing avoltage at said input node to a threshold voltage.
 20. The pointingdevice of claim 19, further comprising a clamp-high circuit, connectedto said node, for clamping said node high in response to a clamp-highcontrol signal.
 21. The pointing device of claim 19, further comprisinga clamp-low circuit, connected to said input node, for clamping saidnode low in response to a clamp-low control signal.
 22. The pointingdevice of claim 19, further comprising a controller, connected to anoutput of said comparison circuit, for generating an output signal inresponse to measuring an amount of time between transitions of saidoutput of said comparison circuit.
 23. A pointing device for use by auser, wherein the user's body provides a ground contact through theuser's finger, the pointing device comprising: a housing for supportingthe user's hand; a pointing sensor, mounted in said housing, forproviding a pointing signal; a stationary scrolling sensor mounted onsaid housing, said scrolling sensor providing a scrolling command inresponse to a movement of the user's finger across said stationarysensor, and continuing to provide said scrolling command in response tosaid finger reaching one end of said stationary scrolling sensor withoutlifting off; wherein said stationary scrolling sensor detects movementof the user's finger using a capacitive sensing circuit comprising asense capacitor, wherein direct galvanic contact by the user's fingercauses the capacitive detection circuit to connect to ground through theuser's body; and wherein said stationary scrolling sensor includes aplurality of discrete electrodes mounted in said housing to detectmovement of a finger, wherein the capacitive detection circuit,connected to said electrodes, for detecting contact of said finger withsaid electrodes, includes: a first, capacitive element, a second elementconnected to said capacitive element, and a comparison circuit, havingan input node connected to said first capacitive element and the secondelement, for comparing a voltage at said input node to a thresholdvoltage.
 24. The pointing device of claim 23, further comprising aclamp-high circuit, connected to said node, for clamping said node highin response to a clamp-high control signal.
 25. The pointing device ofclaim 23, further comprising a clamp-low circuit, connected to saidinput node, for clamping said node low in response to a clamp-lowcontrol signal.
 26. The pointing device of claim 23, further comprisinga controller, connected to an output of said comparison circuit, forgenerating an output signal in response to measuring an amount of timebetween transitions of said output of said comparison circuit.
 27. Thepointing device of claim 3 wherein a circuit, connected to saidelectrodes, for detecting contact of said finger with said electrodes.